1. Department of Biostatistics; University of Liverpool; Liverpool UK
2. Centre for Clinical Practice; National Institute for Health and Care Excellence; Manchester UK
3. Centre for Respiratory Medicine and Allergy, Institute of Inflammation and Repair; University of Manchester and University Hospital of South Manchester; Manchester UK
4. Central Clinical School, Sydney Medical School; University of Sydney; Sydney Australia
5. Discipline of Physiotherapy, Faculty of Health Sciences; University of Sydney; Sydney Australia